1. Field of the Invention
The present invention relates generally to thermoelectric devices, and more particularly to an improved thermoelectric system employing a novel magnesium antimonide semiconductor.
2. Description of the Related Art
Thermoelectric devices have been employed popularly for a many years, largely in connection with temperature regulation systems, such as heating and cooling. Thermoelectric devices of the type involved here are ordinarily solid state devices that function as heat pumps to transfer heat to or from a specific location. Fundamentally they operate under the same principles as do refrigerators or other mechanical heat pumps.
As the skilled artisan will appreciate, the viability of a material to function as a thermoelectric device depends on the efficiency of the material. See, U.S. Pat. No. 5,610,366, hereby expressly incorporated by reference. In that patent, the applicants address the dimensionless figure of merit ZT, which is related to the efficiency of the material to function as a thermoelectric device. That patent also points out how the most popularly employed materials for thermoelectric devices were developed several decades ago. Examples include those listed in that patent as well as Sb.sub.2 Te.sub.3 and Bi.sub.2 Te.sub.3. These materials typically have exhibited a ZT of about 1, and no greater than about 1.2 (under limited operational ranges). Moreover, materials such as Bi.sub.2 Te.sub.3, because of their anisotropic structure, require special processing to produce crystallographically oriented materials.
Particularly in view of technological advances requiring efficient heat transfer (e.g., for space applications, or other sensitive electronic device applications), a need has arisen for an improved material for thermoelectric device, particularly one that exhibits a ZT greater than about 0.4. Further, owing to the broad range of conditions to which the devices will be subjected, it is important for the material to yield consistent and reproducible results through a broad range of operating conditions. It is also desirable to provide a material that can be handled readily and is easy to process, so that impracticalities traditionally associated with manufacture of thermoelectric devices can be avoided.
A discussion of crystal structures for various binary intermetallic phases can be found at Pearson's Handbook: Crystallographic Data for Intermetallic Phases, Desk Edition, Vols. 1 and 2, P. Villars, Ed., ASM International, Materials Park (1997). Heretofore, it is believed that the only reported binary intermetallic phase of Mg.sub.x Sb.sub.y is Mg.sub.3 Sb.sub.2. Mg.sub.3 Sb.sub.2 crystallizes in the trigonal anti-La.sub.2 O.sub.3 structure at room temperature and undergoes a structural transition to a high temperature beta phase that crystallizes in the body centered cubic structure of Mn.sub.2 O.sub.3. Also of potential interest is K. A. Bol'shakov et al., Russian Journal of Inorganic Chemistry, Translated from Zhurnal Neorganicheskoi Khimii, 8, (12), 1418-1424 (1963).